Orlando Police Chief John Mina said the attack began at 2am local time when the club is believed to be filled with as many as 300 people. At 2:09 a.m., a Facebook post from Pulse Orlando said, "Everyone get out of pulse and keep running."

After an exchange of fire with a police officer working at the club, the suspect took hostages. Chief Mina said a decision was taken at 5am to send a SWAT team of 11 police officers who killed the gunman and rescued about 30 hostages.

The gunman has been named as Omar Mateen, a 29-year-old US citizen of Afghan descent who was born in New York and lived in Florida. He was not on a terrorism watch list.

A statement on Islamic State’s affiliated Amaq news agency said that an IS "fighter" was responsible, though the extent of the group’s involvement is not clear.

US President Barack Obama has described Sunday morning's gun attack on a gay nightclub in Orlando, Florida, as "an act of terror and an act of hate.” Americans were united in "grief, outrage and resolve to defend our people", he said.

The Democratic Party's presumptive nominee for president, Hillary Clinton said in a statement: "This reminds us once more that weapons of war have no place on our streets."
"We will keep fighting for your right to live freely, openly and without fear. Hate has absolutely no place in America,” she said in a direct message to the LGBT community.

Mateen’s father told NBC News that his son had become enraged by a gay couple kissing, and the gunman’s ex-wife told the Washington Post that he was an abusive and unstable man.

One witness, Ricardo Almodovar, said on Facebook: “Shooter opened fire @ around 2:00am. People on the dance floor and bar got down on the floor and some of us who were near the bar and back exit managed to go out through the outdoor area and just ran.”

A statement on Pulse’s website by Barbara Poma, owner of the nightclub, reads:

“Like everyone in the country, I am devastated about the horrific events that have taken place today. Pulse, and the men and women who work there, have been my family for nearly 15 years. From the beginning, Pulse has served as a place of love and acceptance for the LGBTQ community. I want to express my profound sadness and condolences to all who have lost loved ones. Please know that my grief and heart are with you.”

A vigil for the victims has been organised in Hong Kong tonight at Pottinger Street’s Linq bar.